port time area and blow down t/a

Joined
Apr 16, 2003
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#1
I have been useing TSR design programs for a while and i have a question ? When i use the "find it"funtion for exhaust blow down t/a the program raises or lowers the transfer ports to arrive at the correct t/a but the amount of height change is too much like 4mm or something like that.I understand that blow t/a should be close to what the pipe is designed and for rpm to hp peak.I also notice that all of the samples of port time area that are in the program that the exhaust, trans and blow t/a are almost exactly what the bmep targets ask for.If i widen the transfers to arrive at the correct t/a target and keep them as low in the cylinder as possible which is more important low port height and total area or blow down t/a?Please clarify to me if a polished exhaust port flows more than a 80grit sanded surface and why?(briefly)Is there any corellation between exhaust port length and choke point and potential for peak hp .eg cr80 cylinder reed engine has a very long port length and can develope about 26hp (useing stock components) and a yz80 case reed engine with a very short port length peaks at about 25hp? thanx
 
Joined
Aug 13, 2000
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#2
I do not use TSR so I cannot comment on the issues you have. However I believe it is safer to enlarge the exhaust port looking for more time area, especially blow down than to use other methods. Changing transfer height by 4mm is just not right.

Chris